Wiring 41 — Dual-Channel E-Stop into a Safety Relay

Dual-channel E-stop into a safety relay

Training material. Follow your site procedures, local electrical code and the manufacturer's instructions. Lockout/tagout and a qualified person are required for real equipment.

Wire the stopping path the way the Industrial Safety track describes it: a two-contact E-stop button, a safety relay that watches both contacts, a reset button, and a contactor that can only be energised through the relay's output contact. Nothing here runs the motor itself; the relay only grants or withholds permission for the contactor coil.

What each part is doing

• Two channels. The button holds two separate normally closed contacts. Each one goes to its own pair of relay inputs. If only one channel opens, or one wire breaks, the relay can notice that the two channels disagree.
• Normally closed. Pressing the button, or losing a wire, removes the signal. The relay drops out and the contactor coil loses its supply.
• Reset. The reset button is a normally open pushbutton on the relay's reset/feedback terminals. Releasing the E-stop must not restart anything on its own; someone has to make a deliberate reset.
• Output in the coil path. Relay output 13/14 sits between +24 V and the contactor coil. Open the contact and the coil cannot pull in.

Your wiring list

1. Bring +24 V and 0 V from the supply to the two rail strips. Bond the supply PE terminal to the ground bar.
2. Power the relay coil supply (A1 to +24 V, A2 to 0 V).
3. Channel 1: +24 V to the relay S11 and to the button NC1-IN; NC1-OUT to S12.
4. Channel 2: +24 V to the relay S21 and to the button NC2-IN; NC2-OUT to S22.
5. Reset: +24 V to the reset button NO-IN; NO-OUT to relay S33; relay S34 to 0 V.
6. Output: +24 V to relay 13; relay 14 to contactor KM1 coil A1; coil A2 to 0 V.

This lab is simplified: it leaves out the contactor auxiliary feedback (external device monitoring) contacts that real installations usually wire into the reset loop, so a welded contactor would not be caught here. It follows the terminal names printed on the simulated relay. Real relays differ (many generate their own test pulses on the S1x/S2x terminals), so always wire from the manufacturer's connection diagram for the exact part.